'Considerable' rating

Hm. Is it bothersome that the lowland weather forecast is, through most of the winter, "mostly cloudy, chance of rain"? 

An avalanche forecast is a moderately complicated weighted integral of past, present, and near future weather.  For the lowland forecast, 'mostly cloudy, chance of rain' is accurate; they're developing the capacity to say, "Cloudy 'till 10 am, sunbreak 'till 11:30, then cloudy again. Drizzle arriving at 3:30, turning to light rain at 4, then back to drizzle. Probably shouldn't have a barbecue."  but it's hard to provide such local specificity in a broad forecast, and confidence in timing and precip amounts is often limited.  So, we get the broadbrush forecast of 'mostly cloudy, chance of rain'.  It's accurate, and fairly precise.

Switching to a lower-resolution rating system for weather, say, "Bomber, Alright, Bad, Horrible", only means that the forecaster gets to anguish over the difference between Alright and Bad a lot of the time, and there are a lot of complaints when it happens to rain on an Alright day or if it happens to be sunny on a Bad day. Having a fifth option, say, "Middling", lets me know that I should bring a raincoat, but that it might be nice. If I want to know more, I'll check out the forecast discussion , where the forecasters can give me hints about what they think might happen.


The more I think about it, the more I like the notion of an avalanche forecast as an aggregation of weather past, present, and future. At its core, it's a complicated weather forecast; can't blame the weatherman for accurately reporting what's going to happen.

The more I think about it, the more I like the notion of an avalanche forecast as an aggregation of weather past, present, and future. At its core, it's a complicated weather forecast; can't blame the weatherman for accurately reporting what's going to happen.

agree...

I don’t think the rating system is broken. Considerable is not difficult to understand and if you think you can relax just because the day is rated moderate or low then its just a matter of time…
This is not the way to look at the rating system. I don’t mean to be harsh, but anyone who dies based on the rating alone is not understanding how to use it in the first place, and would not have mattered how the rating scheme is structured. Everything I have read about incidents involving experienced people indicates a breakdown in group dynamics affecting risk assessment in the field. It only makes sense that the majority of incidents happen in the middle of the rating scale, changing its structure will not change that. People really need to separate the rating from the mitigation and task at hand especially in large groups… if your not certain the slope will not slide the rating (and your complacency with considerable) should not be part of the decision. The rating has NOTHING to do with the stability of the aspect your exposed to in the field…



The important thing to ask yourself when you do not find instability on a considerable day is what were the decisions that affected your outcome? Maybe if you ask that, you will quickly lose your complacency with the “considerable” rating!

Hm. Is it bothersome that the lowland weather forecast is, through most of the winter, "mostly cloudy, chance of rain"? 

An avalanche forecast is a moderately complicated weighted integral of past, present, and near future weather.  For the lowland forecast, 'mostly cloudy, chance of rain' is accurate; they're developing the capacity to say, "Cloudy 'till 10 am, sunbreak 'till 11:30, then cloudy again. Drizzle arriving at 3:30, turning to light rain at 4, then back to drizzle. Probably shouldn't have a barbecue."  but it's hard to provide such local specificity in a broad forecast, and confidence in timing and precip amounts is often limited.  So, we get the broadbrush forecast of 'mostly cloudy, chance of rain'.  It's accurate, and fairly precise.

As the middle rating in the system, I would say that a better comparison in the eyes of those who use an "at a glance" rating system such as from NWAC, would be the ubiquitous "partially cloudy, chance of showers" broadbrush forecast which represents the middle of the road rating we get more than anything around  the NW.  On most days, is there finer grained meteorological data available to make decisions?  Certainly, but most people don't know how, or don't take the time to do so.  No one in the NW ever canceled a BBQ based on a forecast of "partially cloudy, chance of showers".  Instead, you bring a raincoat, tarps, and have a backup plan.  Sometimes you get dumped on, other times it is sunny.  Either way, everyone laughs at how little the weather man or woman knows.

Avy danger and backcountry travel is obviously more serious than a BBQ at Golden Gardens, and considerations made should reflect this.  As has been pointed out, the "considerable" or middle category provides the greatest opportunity to introduce the human factors as discussed in Temper's book.

Most of the comments in defense of the "considerable" rating seem to agree that there is a wide range of variability in what this could mean at any given location, and that a detailed review of available online data, and observable conditions on location are what the backcountry traveler requires to make the best decisions.  While true, this ignores the whole reasoning for creating a traffic light system to begin with, which is that it aims to reach different users who will not, or do not know how to interpret the more detailed information that may be available by simplifying everything.

By virtue of even reading this bulletin board, readers are likely to have some level of avalanche training if not being among the most expert in the region.  It is worth remembering that avalanche training experts are not the target audience for the NWAC traffic light rating system.

Disagree, Does a green light mean it’s safe to enter the intersection? The rating system is not a go-no go gage and should be taught separate from the risk mitigation at hand.

"what is the effectiveness of a rating that constitutes a large portion of the ratings listed during days in areas where avi fatalities occur?"

It's very effective. There are lots of days where considerable does, generally, describe the day's avy risk. Changing the terms will not decrease the number of days with considerable risk. Reducing the rating resolution will not help folks who fundamentally base their decisions on a forecast.

NWAC isn't an oracle. There is simply no general answer to "is it safe out there?"

I think my frustration is with this rating change tack to reducing avy fatalities. There very well may be a better rating system possible. I doubt it would save lives. Certainly not the recent sad losses we've had in WA and probably not those in CO.

There is a risk in leading the general public to a conclusion that the NWAC ratings could have been better and therefore a forecast tweak will save lives. Its a passive conclusion that doesn't require any change in behavior. The better takeaway is that people should be awed and appropriately fearful of nature and our snowpack.

The discussions around group dynamics and decision making are much more likely to bear fruit. Our energy is better spent there.

Chuck, some "criers" have loads of experience in a variety of snowpacks.  I simply ask the question, "what is the effectiveness of a rating that constitutes a large portion of the ratings listed during days in areas where avi fatalities occur?"

Although it is true most avalanche accidents happen in Considerable hazard I think one needs to look at the reasons behind the statistics. In Moderate hazard forecasters would tell you that they expect few reports of incidents, none most commonly on a Moderate day. So people don't get caught very often. I really only worry about Moderate hazard if there is a generally stable snowpack but one that has historically had bad layers, near wind-loaded features usually above treeline, or in warm weather. In High hazard there is enough public information out there (backcountry travel is not recommended) that few venture out. So there aren't as many accidents. In High hazard with an expectation of good skiing to make it worthwhile, I'll usually ski in safe forests. But in Considerable hazard people do venture out. Forecasters would tell you that they expect to hear of some incidents and there is still significant hazard. So, it is not surprising that there are more accidents in Considerable hazard. The word "consider" is the root of Considerable.

But much more important than the level of the hazard is the text describing the situation from an avalanche perspective. It is here that you'll appreciate recent reports of avalanches or highly unstable snow. It is in the text (and the supporting telemetry) that you'll appreciate the significance of recent wind-loading, and of particularly troublesome weak layers like icy crusts, facets, and surface hoar. The text is the key beginning element to arm yourself with in discussing with your friends an appropriate choice of a tour on a particular day.